Maybeshewill have done a top 10, which got me thinking what my top 5 might be
http://www.musicradar.com/news/guitars/maybeshewills-10-favourite-instrumental-bands-605424

First attempt:
1. Nils Frahm
2. Explosions in the Sky
3. Max Richter (unless the spoken samples make him ineligible)
4. Eluvium
5. Luke Abbott